DESCRIPTION (Adapted from Abstract): Dr. Boettcher will conduct a series of experiments to investigate the additivity of age-related and noise-induced hearing loss in the gerbil. Animals will be raised in a sound-isolating environment, and hearing testing will be performed on each ear before and after exposure of a single ear to noise at a level intended to produce a mild hearing loss. Dr. Boettcher will investigate whether susceptibility to noise-induced hearing loss varies as a function of age, and whether a non- traumatic conditioning sound can reduce the magnitude of age- related hearing loss. Dr. Boettcher will measure auditory threshold using auditory brainstem responses, and will also, in a subset of animals, obtain measures of histopathology of the stria vacularis, hair cells and eighth nerve fibers.